Monday, 19 May 2014

Big progress!

Quite an eventful time since my last update. I completed the second half of the plaster mould for making the intake manifold runner wax plugs. Unfortunately, of all the words I could use to describe the first trial, ‘successful’ does not even register! From my previous experiment, I learned that the mould needs to be warm otherwise the wax chills too quickly and leaves a very poor surface finish. This time around, I discovered that the plaster was so absorbent that is ‘drank’ virtually all of the liquid wax before it could freeze. As well as failing to make a wax plug, this meant that the mould surface was now waxy and I could not get any sealant to stick to it! I therefore had to rethink the all-plaster method and reverted back to the silicone and plaster ‘mother mould’ technique. This time however, I used a higher hardness silicone that holds its shape much better than the first material I trialled. Building on the first all-plaster mould, I also revised the closing box shape to lose a lot of the unnecessary volume. This made for a lighter part to ease handling, as well as minimising the face area of the tool, thereby reducing the chances of debris getting caught between the two halves and distorting the cavity alignment.

I started the mould by creating a wall around the plug into which I poured the silicone. This takes 24 hours to cure, then I added the registration markers (the black 'dots') and assembled the wooden case for pouring the plaster.

With this part cured, I could de-mould it, turn it over then apply Vaseline as a release agent to the first silicone half. I then built a a further plasticine wall before pouring the second half of the silicone

After 3 coats of mould release 'soap' to act as a barrier, this could then be boxed up to pour the second half of the plaster.

Finally, the mark 2 version of the mould is ready. I left it a week (with the two mould halves bound together to minimise distortion) allowing the majority of the moisture in the plaster to evaporate.

Nothing left now but to pour in the wax and hold a piece of dowel in place to act as a handle

The first part out of the mould  did not have a great surface finish, mainly due to the moisture still present in the plaster part of the mould condensing inside the cavity (despite the week I gave it to dry out). Further wax parts have greatly improved upon this as the plaster has dried out even more

With a usable wax master, I have been able to lay up a trial carbon fibre runner with a schedule of 2 layers of gel coat followed by 4 layers of carbon sleeve covered in a coated heat shrink tube for consolidation, all cured at room temperature. The post cure cycle (vital for parts exposed to elevated temperatures) even allowed the wax core to melt out as planned. There were a few cosmetic issues with this first part – a couple of runs in the gel coat and learning the best way to apply the sleeve layers – meant a less than ideal weave pattern on the outside. In addition, the heat shrink is very thin and therefore was a little tricky to work with (i.e. I burned a couple of holes in it before I turned down the wick on the heat gun!). This, along with the less than ideal internal surface finish from the first off wax, meant this was a sacrificial part only suitable for cutting up to see how well the composite had been laminated. I am pleased to report only a few small inclusions in the thickness of the wall and a couple of bubbles under the gel coat which should be avoidable with better consolidation between applying layers of sleeve. I have enough materials for a second trial (along with the 8 ‘good’ parts needed for the job), but hopefully I won’t need to cut up another one! Eight more to go then.

Other big news is that the body shell is finally complete and last week I travelled up to Newark to collect. I am very pleased with the colour combination and the photos don’t do it justice – bear in mind it is straight out of the mould with no polishing. Unfortunately, in all the excitement of getting it off the back of the Luton van (thanks for the additional muscle power, Neil!) I neglected to get a proper picture of it. The body will remain on its stand whilst I work inside the engine bay, then It can be mated with the chassis before carrying on assembly. I should then be able to get a good photo or two when it rolls out into the sun light as a (sort of) complete car!

First job is to apply stone chip to the inside of the wheel arches. Not the most glamorous of jobs, getting spattered in liquid rubber and cross eyed from the fumes, but 2 coats later, it is complete.

Next up is the fitting of the various panels - 2 in the wheel arches, bonnet and boot. This should keep me entertained for a little while!

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